1. Technical Field
The present invention relates generally to semiconductor fabrication, and more particularly, to methods for supercritical development or removal of block copolymer for patterning applications. In addition, the invention relates to removal of poly(methyl methacrylate-b-styrene) (PMMA-b-S) based resists using a polar supercritical solvent.
2. Related Art
The use of bottom-up approaches to semiconductor fabrication has grown in interest within the semiconductor industry. One such approach utilizes block copolymers for generating sub-optical ground rule patterns. In particular, one illustrative use is forming a ‘honeycomb’ structure with in a poly(methyl methacrylate-b-styrene) (PMMA-b-S) block copolymer. In the case of a cylindrical phase diblock having a minor component of PMMA-b-S, the PMMA-b-S block can phase separately to form vertically oriented cylinders within the matrix of the polystyrene block upon thermal anneal.
FIGS. 1A-C show the above-identified approach. FIG. 1A shows a substrate 10 coated (optionally) with a random copolymer 12, which is affixed to the surface. A block copolymer 14 is then coated on the top surface of the stack, as also shown in FIG. 1A. Block copolymer 14 is annealed with heat allowing for phase separation of the immiscible polymer blocks 18 and 20, as shown in FIG. 1B. As shown in FIG. 1C, the annealed film is then developed (perhaps augmented by using actinic irradiation) to reveal a pattern 30 that is commensurate with the positioning of one of the blocks in the copolymer. For simplicity, the block is shown as completely removed although this is not required.
Since block copolymers have a natural length scale associated with their molecular weight and composition, the morphology of a phase-separated block copolymer can be tuned to generate cylinders of a specific width and on a specific pitch. In one approach, ultraviolet (UV) exposure is used to cause the PMMA to decompose (and polystyrene to crosslink) into smaller molecules and, further, developed using glacial acetic acid to remove the small molecules. In other approaches, development simply uses the acetic acid to reveal the pattern.
For most applications, and in particular bottom-up semiconductor fabrication methodologies, the pattern must be transferred to a substrate. FIGS. 2A-B show a representative procedure in which a substrate 40 and a dielectric material 42 deposited upon it are (optionally) coated with a random copolymer 44, which is affixed to the surface. As shown in FIG. 2A, a block copolymer film 46 is coated on the top surface of the stack, annealed with heat allowing for phase separation of the immiscible polymer blocks, and developed to reveal a pattern having one block 48 remaining as a mask and voids 50 commensurate with the position of a second block of copolymer film 46. Again, for simplicity, the block is shown as completely removed although this is not required. This patterned copolymer film 46 is then used as a mask to transfer into underlying dielectric material 42. As shown in FIG. 2B, the resulting patterned dielectric material 52 is commensurate with the original pattern in copolymer film 46. This type of pattern has been shown, when applied to cylindrical phase PMMA-b-S, to allow for increased surface area, which increases capacitance in storage applications as well as provides ‘quantized’ wells for flash memory.
While these approaches demonstrate the capability of bottom-up fabrication, there are challenges with respect to implementation in a conventional semiconductor fabrication facility. One challenge relative to the implementation of this particular diblock copolymer is the development of PMMA-b-S without damaging a surrounding matrix while maintaining manufacturing compatible processes. In particular, the conventional approaches use glacial acetic acid to remove the PMMA-b-S using batch processing or liquid coating. Glacial acetic acid implementation requires specialized tooling in order to handle its flammability and corrosiveness. In other approaches, isopropyl alcohol (IPA) is utilized to develop PMMA-b-S e-beam resist. Unfortunately, IPA is not sufficient to remove an unexposed PMMA-b-S film having molecular weights and compositions of interest for semiconductor fabrication. Additionally, in some circumstances a 25 J/cm2 UV exposure is used to develop the block copolymer, which is roughly 1000 times greater than that used for conventional resist.
Another challenge in the semiconductor industry is removing PMMA-b-S-based resist. In particular, plasma stripping of PMMA-b-S-based resist can damage porous interlayer dielectrics in certain integration schemes.
In view of the foregoing, there is a need in the art for methods of developing and/or removing select regions of block copolymers that do not suffer from the problems of the related art. In addition, there is a need in the art for a method of removing PMMA-b-S-based resist without damaging porous interlayer dielectrics.